The subject matter disclosed herein relates to vibration cancellation systems for, for example, rotary wing aircraft.
Rotating machinery commonly produces vibration. Rotary wing aircraft, for example, are susceptible to vibration even with correctly balanced and tracked components, such as rotors. This is due, at least in part, to oscillatory aerodynamic loading which produces forces and moments of vibratory load along three axes (X,Y,Z) which are generated by the rotor at the blade passing frequency. The forces and moments are usually transmitted through the shaft, aircraft transmission, and into the airframe via transmission attachments to produce vibration in the airframe. The goal of vibration cancellation is to reduce vibration to an acceptable level for occupant comfort and component reliability.
One typical approach to reducing such vibration involves replacing a rigid gearbox mounting strut with a compliant strut and parallel hydraulic actuator. Such an arrangement intercepts the vibration of the gearbox before the vibration is transferred to the airframe, and/or it generates counteracting loads to partially suppress the vibration. Interruption of the load path between the gear box and the airframe may cause fatigue failures in engine drive shafts which transmit power to the gear box.
Another conventional approach utilizes counter-rotating eccentric masses located in the airframe to rotate at the frequency of the aircraft vibration. A second pair of eccentric masses phased relative to the first pair to yield a force magnitude from zero to maximum force. Rotation of the masses is controlled to counter the vibratory forces entering the airframe from the gearbox. Typical force generators are driven by sizeable electric motors and since each unit can counteract one of the six moments and forces driving the vibration, six such units are required to have full vibration control capability.
The art would well-receive an improved, more compact vibration cancellation system for a rotary wing aircraft.